There is a molecule in your blood that builds muscle, strengthens bones, repairs tissue, and keeps you feeling vigorous. There is also strong evidence that having too much of it accelerates aging and increases cancer risk.
Same molecule. IGF-1 — insulin-like growth factor 1.
This paradox makes IGF-1 one of the most fascinating and debated biomarkers in longevity science. Understanding where you want your levels to be is not straightforward — it requires balancing short-term performance with long-term aging.
What IGF-1 is
IGF-1 is a hormone produced primarily by the liver in response to growth hormone (GH) from the pituitary gland. When GH arrives at the liver, the liver releases IGF-1 into the bloodstream, where it acts on cells throughout the body.
IGF-1 is the mediator of most of growth hormone's effects. When people talk about "growth hormone benefits," they are largely talking about IGF-1 downstream.
What IGF-1 does:
- Stimulates protein synthesis — building muscle tissue
- Promotes bone growth and density
- Enhances tissue repair — wound healing, connective tissue recovery
- Supports brain health — neurogenesis, synaptic plasticity
- Stimulates cell proliferation — this is the double-edged sword
That last point is the crux of the longevity paradox. Cell proliferation is great when you are growing, healing, or building muscle. But cell proliferation also means cells divide more — and every cell division is an opportunity for a DNA mutation that could eventually become cancer.
IGF-1 levels by age
IGF-1 peaks during puberty and declines steadily with age:
| Age | Typical IGF-1 range (ng/mL) |
|---|---|
| 14–18 | 200–900 |
| 18–25 | 150–400 |
| 25–35 | 115–350 |
| 35–45 | 100–300 |
| 45–55 | 90–270 |
| 55–65 | 80–240 |
| 65+ | 70–220 |
These ranges are wide because IGF-1 is influenced by genetics, nutrition (especially protein intake), exercise, sleep, liver function, and hormonal status.
The longevity paradox
The case for lower IGF-1
Animal studies provide the strongest evidence. Mice, worms, and flies with genetically reduced IGF-1 signaling consistently live 15–40% longer. The Laron dwarfs — a population in Ecuador with a genetic mutation that renders them unable to respond to growth hormone (and thus have very low IGF-1) — have dramatically lower rates of cancer and diabetes despite obesity and other risk factors.
Human epidemiological data supports this pattern with more nuance:
- The European EPIC study found that higher IGF-1 was associated with increased risk of prostate, breast, and colorectal cancer.
- The Nurses' Health Study found similar associations for breast cancer.
- Population studies of centenarians have found that many have relatively low IGF-1 levels compared to younger cohorts.
The mechanism: IGF-1 activates the mTOR pathway — a master cellular growth switch. mTOR promotes protein synthesis and cell growth but suppresses autophagy (the cellular recycling process that removes damaged proteins and organelles). High IGF-1 means high mTOR, which means cells are in "growth mode" and less in "clean-up mode." Over decades, this may accelerate accumulation of cellular damage.
The case for adequate IGF-1
Very low IGF-1 is not without consequences:
- Sarcopenia — accelerated age-related muscle loss
- Osteoporosis — reduced bone mineral density
- Cognitive decline — IGF-1 supports brain-derived neurotrophic factor (BDNF) and neurogenesis
- Poor wound healing and immune suppression
- Frailty — the leading cause of loss of independence in older adults
Studies in older adults show that very low IGF-1 (below the 25th percentile for age) is associated with increased frailty, falls, and all-cause mortality. There appears to be a U-shaped relationship: both very high and very low IGF-1 carry risk.
The sweet spot
Most longevity-focused physicians — including Peter Attia — target the lower half of the age-adjusted normal range, typically:
- 100–180 ng/mL for adults aged 30–60
- 80–150 ng/mL for adults aged 60+
The goal is enough IGF-1 to maintain muscle, bone, and brain health, but not so much that you are chronically driving mTOR-mediated cell proliferation.
What influences IGF-1 levels
Protein intake
The strongest dietary driver of IGF-1 is protein, particularly animal protein. The amino acid leucine (abundant in meat, dairy, and eggs) is a potent IGF-1 and mTOR stimulator. Reducing protein intake — particularly from animal sources — is one of the most reliable ways to lower IGF-1.
Valter Longo's research suggests that moderate protein restriction (0.7–0.8 g/kg body weight per day) in middle-aged adults may be beneficial for longevity, while higher protein (1.0–1.2 g/kg) becomes important after age 65 to prevent sarcopenia.
Fasting and caloric restriction
Fasting lowers IGF-1 significantly. Longo's fasting-mimicking diet (5 days of reduced calories) has been shown to lower IGF-1 by 20–40%. Chronic caloric restriction also lowers IGF-1, as demonstrated in the CALERIE trial.
Exercise
Resistance training acutely spikes IGF-1 (which is partly how it stimulates muscle growth). Regular aerobic exercise has a more complex effect — it may modestly lower baseline IGF-1 while improving IGF-1 sensitivity.
Sleep
Growth hormone — and therefore IGF-1 production — is heavily dependent on deep sleep. Poor sleep, particularly reduced deep sleep, lowers IGF-1 over time.
Liver health
The liver produces roughly 75% of circulating IGF-1. Liver disease, fatty liver, or chronic alcohol use can impair IGF-1 production.
How to think about your IGF-1
The practical framework:
If your IGF-1 is high (above the 75th percentile for your age):
- Consider reducing animal protein intake or cycling with periods of lower protein
- Periodic fasting or fasting-mimicking diets
- Ensure you are getting cancer screenings appropriate for your age
If your IGF-1 is low (below the 25th percentile for your age):
- Ensure adequate protein intake (at least 1.0 g/kg body weight)
- Optimize sleep — particularly deep sleep
- Rule out liver disease, malnutrition, or thyroid issues
- Consider whether caloric restriction has gone too far
If your IGF-1 is in the middle range: likely optimal. Monitor annually.
How Merios helps
Upload your IGF-1 results to Merios alongside your metabolic panel (fasting insulin, HbA1c), liver markers (ALT, AST), and Apple Watch data (deep sleep, exercise). Track how dietary changes, fasting protocols, and exercise affect your IGF-1 over time. The trend is what matters.
Track your IGF-1 with Merios →
This article is for informational purposes only and does not constitute medical advice. Discuss IGF-1 levels and longevity strategies with your physician.